Method of producing polyhydric compounds

ABSTRACT

A polyhydric compound is produced by catalytically disproportionating a precursor which is a lower carboxylate ester of said compound containing at least one lower carboxylate group and at least one free hydroxyl group. Most preferably the invention relates to the production of a diol by the catalylic disproportionation of a lower carboxylate diester of the diol.

This is a division of application Ser. No. 178,588, filed Sept. 8, 1971,now U.S. Pat. No. 3,859,368.

This invention relates to the treatment of lower carboxylate esters ofpolyhydric compounds, especially diols and triols, wherein the esterscontain at least one lower carboxylate group and at least one freehydroxyl group, and is more particularly concerned with the preparationof diols, especially ethylene glycol, by catalytic disproportionation oflower carboxylate monoesters of such diols.

Diols and triols are known compounds, many of which are producedcommercially in substantial quantities. Thus, ethylene glycol, forexample, is a chemical of acknowledged commercial importance which isused primarily in the preparation of anti-freeze compositions and in themanufacture of polyester fibers. Ethylene glycol manufacturing processesof commercial interest have generally been based upon the use ofethylene oxide as a raw material. Recently, however, processes have beendeveloped which make it possible to produce diols such as ethyleneglycol and propylene glycol without the necessity for the intermediatemanufacture of the oxide. These processes employ the liquid phasereaction of the appropriate olefin, a carboxylic acid, and molecularoxygen in the presence of a catalyst to produce carboxylic acid estersof the glycol. A process of this type is disclosed in Belgian Pat. No.738,104. The glycol can be liberated by hydrolysis of the carboxylateesters produced in such processes. However, the hydrolysis reactionpresents certain problems from the standpoint of efficiency and maximumconversion to the desired glycol. Related problems arise in connectionwith the production of other polyhydric compounds.

It is an object of this invention to provide an improved process for theproduction of a polyhydric compound from a precursor which is a lowercarboxylate ester of the polyhydric compound and contains at least onelower carboxylate group and at least one free hydroxyl group.

It is another object of the invention to provide a process of thecharacter indicated which can be combined with the preparation ofethylene glycol by the hydrolysis of lower carboxylate esters ofethylene glycol.

It is an additional object of the invention to provide a process whichcan be used to produce additional amounts of ethylene glycol from thepartial hydrolyzation of lower carboxylate esters of ethylene glycol.

Other objects of the invention will be apparent from the followingdescription of the invention and of illustrative embodiments thereof.

In accordance with the invention, lower carboxylate esters of dihydricand tridhydric alcohols, i.e. diols and triols, containing 2 to 6 carbonatoms, which esters contain at least one lower carboxylate ester groupand at least one free hydroxyl group, especially lower carboxylatemonoesters, are heated in the presence of a catalyst which can begenerally characterized as a weak base. It has been discovered that inthis environment the lower carboxylate ester undergoes, without the needfor the presence of an extraneous reactant, what may be characterized asa disproportionation reaction to produce the free polyhydric alcohol,e.g. ethylene glycol, and the corresponding lower carboxylate ester ofthe polyhydric alcohol which has an added lower carboxylate group, e.g.the lower carboxylate ester of ethylene glycol, as illustrated in thefollowing equations:

    2 diol monoester → diol + diol diester

    2 triol monoester → triol + triol diester

    3 triol diester → triol + 2 triol triester

Esters which may be treated in accordance with the invention to producethe corresponding free polyhydric alcohols are the lower carboxylateester of diols or triols which are the hydroxy derivatives of saturatedacyclic or cyclic hydrocarbons or unsaturated acyclic or cyclichydrocarbons. As indicated, the hydrocarbon radical of such diols ortriols may contain 2 to 6 carbon atoms, preferably 2 to 4 carbon atomsin the case of acyclic compounds, and 6 carbon atoms in the case ofcyclic compounds. Examples of such esters are the lower carboxylatemonoesters of diols such as ethylene glycol, 1,2-propane diol(propyleneglycol), 1,3-propane diol, 1,4-butane diol, 1,2-butane diol,1,2-cyclohexane diol, 1,4-butene diol, 1,2-butene diol, catechol(1,2-benzenediol), resorcinol( 1,3-benzenediol), and hydroquinone(1,4-benzenediol), and the lower carboxylate mono- and diesters of triolssuch as glycerol and 1,2,3-trihydroxy butane.

In the following discussion of the invention, the process will bedescribed and exemplified with particular reference to esters ofethylene glycol, especially ethylene glycol monoacetate, but the processis equally applicable to esters of other diols and triols as definedabove, the discussion in terms of esters of ethylene glycol being solelyfor convenience and ease of description. It is known that ethyleneglycol carboxyklate monoesters will undergo hydrolysis in the presenceof water and in the presence of an acidic catalyst to produce ethyleneglycol and the corresponding carboxylic acid, as disclosed, for example,in Belgian Pat. No. 738,104, and it is also known that in the presenceof ethanol or methanol, ethylene glycol esters will react with thealcohol to produce ethylene glycol along with an ester of the alcohol,as disclosed, for example, in U.S. Pat. No. 1,454,604. Thedisproportionation of this invention, however, is different from suchprocesses and, indeed, the process of the invention can be applied tothe products of these prior processes in order to produce additionalquantities of ethylene glycol.

The lower carboxylate ester which is treated in accordance with thisinvention is an ester of the appropriate diol or triol and an alkanoicacid having from 1 to 6 carbon atoms per molecule, such as formic acid,acetic acid, propionic acid, butyric acid, isobutyric acid, and thevaleric and the caproic acids, the ester being a monoester in the caseof diols, and a monoester or a diester in the case of triols.Accordingly, the lower carboxylate monoesters of ethylene glycol towhich the process of this invention is applicable include ethyleneglycol monoformate, ethylene glycol monoacetate, ethylene glycolmonopropionate, ethylene glycol monobutyrate, ethylene glycolmonoisobutyrate, the ethylene glycol monovalerates and the ethyleneglycol monocaproates. Ethylene glycol monoformate, ethylene glycolmonoacetate, monopropionate, monobutyrate and monoisobutyrate, andmixtures of such monoesters with the corresponding diester, areespecially desirable feedstocks, and the monoacetate and thediacetate-monoacetate mixtures are the preferred feedstocks. Of course,mixtures of esters such as mixtures of ethylene glycol monoacetate andethylene glycol monopropionate, as well as mixtures with one or morediesters, including mixed diesters such as ethylene glycol acetatepropionate, also can be employed. As used herein, therefore, the term"ester feed" is intended to include not only the lower carboxylateethylene glycol monoester alone but also mixtures with the correspondingdiester, and mixed esters, as well as mixtures of different ethyleneglycol carboxylate esters. In general, mixtures of the monoester with adiester may contain varying amounts of the corresponding lowercarboxylate diester of ethylene glycol, e.g. up to about 85 mol percentof the diester or diesters, based on the combined monoester-diestercontent of the mixture. Aside from the mono- and diesters, small amountsof by-products associated with the preparation of the glycol ester mayalso be present. Such by-products would normally include smallquantities of ethylene glycol itself, water and acids, as well asunreacted lower carboxylic acid. They may also include catalyst residuesand aldehydic by-products, such as, for example, acetaldehyde andformaldehyde. Thus, the effluent from the reaction wherein the monoesteris produced can be processed as such in the disproportionation reactionof this invention. Typical reaction effluents of this nature aredescribed, for example, in the above-mentioned Belgian Pat. No. 738,104,wherein the monoester is produced in the presence of substantialquantities of the diester, and in British Pat. No. 1,124,862, whereinthe production of monoester substantially free from diester isdisclosed. This invention, however, is applicable to glycol estersproduced in any manner, whether by the process of the Belgian patent orthe British patent or by various other processes. Further, the esterfeed may comprise the effluent from the hydrolysis of ethylene glycollower carboxylate esters, since even when only lower carboxylatediesters of ethylene glycol are hydrolyzed, the monoesters are formedduring the course of the hydrolysis. It is generally preferable topurify such reaction and hydrolysis effluents to remove low-boilingmaterials, such as water and carboxylic acid, prior to subjecting theglycol ester to disproportionation. The invention is thus in no waylimited to feeds comprising ethylene glycol monoesters from anyparticular source. In like manner, the invention is applicable to thecorresponding lower carboxylate esters and ester mixtures of other diolsand of triols of the character indicated above.

To provide the catalyst suitable for use in the disproportionationreaction of the invention there is used a compound which is a weak basein itself, or a substance which forms a weak base in situ in thepresence of ethylene glycol carboxylate esters. For example, there maybe used:

a. metals and metal compounds, such as lithium, sodium, potassium,calcium, beryllium, magnesium, zinc, cadmium, strontium, aluminum, lead,chromium, molybdenum, manganese, iron, cobalt, germanium, nickel,copper, mercury, tin, boron, antimony, bismuth, and cerium as the metal,or as an oxide, hydride, carboxylate such as formate or acetate,alcoholate, or glycolate, or metal alkyl, for example tetrabutyl tin,cadmium acetate, lead acetate, zinc acetate, and dibutyl tin diacetate,

b. Tertiary amines, such as trimethyl amine, triethylene diamine, anddimethyl stearyl amine,

c. Quaternary ammonium salts of weak acids, such as tetramethyl ammoniumacetate.

The preferred type of catalyst is that of group a) above, and thepreferred individual catalysts are carboxylates of tin, lead, zinc,magnesium and cadmium, especially the acetates.

The amount of catalyst employed can vary, so long as there is an amounteffective to cause the reaction to proceed. A generally suitablequantity is from 0.001 to 5.0% by weight based upon thefree-hydroxy-group-containing ester in the ester feed to thedisproportionation zone. Preferably, the amount of catalyst is 0.01% to1.0% and a particularly preferred quantity is 0.1 to 0.5%. Greaterquantities can be used, the maximum amount being generally limited byeconomic considerations. The catalyst, if desired, can be added directlyto the disproportionation zone, but the catalyst is preferably added tothe ester feed prior to its introduction into the disproportionationzone. The residence time of the reactants in the disproportionation zonecan also vary and, since increased residence times favor increasedconversion of the ester to the polyhydric compound, a residence timesufficient to effect a reasonable conversion should be employed, e.g. atleast about 0.25 minutes and, in general, the maximum residence time isgoverned only by the economics of the system. Preferably, however, aresidence time of at least 2 minutes should be employed and, as ageneral rule, residence times longer than 50 minutes are notparticularly useful.

While the disproportionation reaction will take place at ambienttemperature, e.g. room temperature, the reaction is favored by heat andit is preferred, therefore, that the reaction be carried out at atemperature of at least about 100°C. In any case, the temperature shouldbe above the melting points of the polyhydric compound and estercomponents of the reaction system. Ordinarily, temperatures greater than280°C. are not necessary although higher temperatures can be employed ifdesired.

Pressure is not a parameter of the reaction and atmospheric,subatmospheric and superatmospheric pressures may be employed asdesired. Obviously minimum and maximum pressure will be related to thetype of apparatus available and as a general rule there is notparticular advantage in operation at pressures less than 50 mm. Hg orgreater than 250 psig.

The polyhydric compound thus produced is separated from the reactionmixture in any convenient manner, as by extraction with a selectivesolvent or by distillation, e.g. extractive or, especially in the caseof ethylene glycol and propylene glycol, use may be made of azeotropicdistillation as described in the co-pending application of Richard L.Golden entitled "Recovery of Alkylene Glycols" and filed on even dateherewith and now U.S. Pat. No. 3,809,724. In the case of solventextraction or extractive distillation there is suitably used ahigh-boiling compound which is inert with respect to the reactionmixture, such as a hydrocarbon or other non-polar or mildly-polarmaterial such as an ether. The extracting solvent will be liquid underthe prevailing conditions and will most suitably have a boiling pointwhich is 50°C. or higher than the boiling point of the dicarboxylate,e.g. ethylene glycol diacetate, in the reaction mixture. A typicallysuitable hydrocarbon is dodecane, and a typical extracting ether isdiphenyl ether. The disproportionation and the separation of the productdiol or triol can be carried out individually in different zones but oneof the important advantages of this invention is that thedisproportionation reaction can be effected simultaneously with theseparation operation. Thus, the disproportionation reaction can beeffected continuously in a distillation or extraction zone, e.g. afractional distillation column, with continuous introduction of esterfeed and continuous removal of product diol or triol as it is produced.The concurrent extraction or distillation taking place in thedisproportionation zone has the effect not only of providing for therecovery of the desired polyhydric compound from the reaction mixturebut, as will be apparent from the equation referred to above, suchremoval of polyhydric compound favors the reaction itself. Thus whenazeotropic distillation is employed as described in co-pendingapplication, and this is of particular use in the case of ethyleneglycol and propylene glycol, any azeotroping agent which will form aminimum-boiling azeotrope with the polyhydric compound and which can beseparated by fractional distillation from any other azeotrope which maybe formed, and from other components of the system, and which isessentially water-immiscible, can be used and this embodiment,therefore, is not limited to any particular agent but it is preferred,from the standpoint of ease of operation, to employ an azeotroping agentwhich forms a minimum-boiling azeotrope with the polyhydric compound andwhich has a boiling point at atmospheric pressure of 135° to 190°C.,preferably 150° to 170°C. When the mixture undergoing disproportionationis concurrently distilled in the presence of azeotroping agents such asagents of the character indicated, the resulting polyhydric compoundazeotrope with the azeotroping agent can readily be removed from thesystem by distillation and the polyhydric compound can be readilyrecovered. The azeotrope, when condensed, separates into two phases,viz. a phase composed essentially of the azeotroping agent and a phasecontaining the polyhydric compound. The phase containing the azeotropingagent is readily separated, as by decantation, from the polyhydriccompound-containing phase and is returned to the distillation zone, i.e.the zone in which the disproportionation reaction is taking place underdistillation conditions, as reflux. Consequently, the azeotroping agentis merely recirculated in the system and the originally-suppliedquantity of azeotroping agent is continuously available for reuse.

Suitably the azeotroping agent has a boiling point within theabove-indicated 135° to 190°C. range at atmospheric pressure, mostadvantageously within the specified preferred temperature range, but itpreferably also forms a minimum-boiling azeotrope which has a boilingpoint which differs by at least 5°C. from the boiling point at the samepressure of the azeotropes formed by the polyhydric compound with any ofthe carboxylate esters of the polyhydric compound present in themixture. Particularly suitable as azeotroping agents are the saturatedhydrocarbons, both acyclic and cyclic, having boiling points within thespecified range, the aromatic hydrocarbons, and those which have therequired boiling points at atmospheric pressure within the range of 135°to 190°C. are, for the most part, alkyl-substituted benzenes,halogenated hydrocarbons, especially halogenated aromatic hydrocarbons,ethers, ketones and alcohols, and an especially preferred azeotropingagent is pseudocumene. As disclosed in said co-pending application,agents of this character include the following (Table A); wherein theboiling points of the ethylene glycol azeotropes are indicated.

                  TABLE A                                                         ______________________________________                                                         Azeotrope   Agent                                                             b.p.,°C.                                                                           b.p.,°C.                                  Azeotroping Agent                                                                              760 mm.Hg   760 mm.Hg                                        ______________________________________                                        Ethylbenzene     133         136.2                                            Cumene           147         152.8                                            Anisole          150.5       153.9                                            Bromobenzene     150.2       156                                              1-Bromohexane    150.5       156                                              1,2,3-Trichloropropane                                                                         150.8       156.9                                            Propylbenzene    152         159                                              o-Chlorotoluene  152.5       159                                              2,7-Dimethyl Octane                                                                            153         160                                              p-Chlorotoluene  155         162                                              Mesitylene       156         164.6                                            1,3-Dibromopropane                                                                             160.2       167.3                                            2,6-Dimethyl-4-Heptanone                                                                       164.2       168                                              Pseudocumene     158         169.5                                            Phenetole        161.5       172                                              m-Dichlorobenzene                                                                              166         172                                              2-Octanone       168         172.9                                            Benzylmethyl Ether                                                                             159.8       174                                              Decane           161         174                                              p-Dichlorobenzene                                                                              163         174                                              Heptyl Alcohol   174.1       177                                              p-Cymene         163.2       177                                              p-Methylanisole  166.6       177                                              bis-(2-chloroethyl)ether                                                                       171         178                                              o-Dichlorobenzene                                                                              165.8       179                                              ______________________________________                                    

As disclosed in said co-pending application, some typical agents whichform minimum boiling azeotropes with propylene glycol include o-xylene(azeo. b.p. 135.8°C.), dibutyl ether (azeo. b.p. 136°C.) and 2-octanone(azeo. b.p. 169°C.).

The polyhydric compound containing phase from the azeotropic condensateis subjected to further distillation to remove as overhead the ethyleneglycol monocarboxylate ester and a relatively small amount of thepolyhydric compound, along with any azeotroping agent which may bepresent, and substantially pure ethylene glycol is withdrawn as bottomsproduct. The glycol-rich phase from the extractive distillation can besimilarly treated. The overhead product from this last-mentioneddistillation step is advantageously combined with the feed to thedistillation column.

As previously mentioned, the ester disproportionation process of thisinvention is particularly adapted to be integrated with the hydrolysisof lower carboxylate esters of the polyhydric compound, e.g. ethyleneglycol lower carboxylate monoesters, diesters and mixtures of monoestersand diesters, i.e. it can follow the hydrolysis operation in order toproduce additional quantities of polyhydric compound. Thus, illustratingthe hydrolysis operation by the case of ethylene glycol, which isrepresentative of the other polyhydric compounds within the scope of theinvention, not only can the ester feed to the disproportionationreaction consist essentially of ethylene glycol lower carboxylatemonoester alone or in admixture with ethylene glycol lower carboxylatediester along with minimum amounts of other materials which may bepresent as a result of the manufacturing process by means of which theesters are produced but the ester feed may also comprise the effluentfrom the partial hydrolysis of ethylene glycol carboxylate esters,suitably after removal of water and carboxylic acid, which effluent willcontain not only the ethylene glycol monoester and generally theethylene glycol diester, but will also contain varying amounts ofethylene glycol itself. The hydrolysis of ethylene glycol esters is anequilibrium reaction and to obtain high ester conversion wouldconventionally require the use of large excesses of water, therebysharply reducing the concentration of the reaction mixture andcomplicating recovery procedures. It is advantageous, therefore, unlessspecial hydrolysis techniques are employed, to limit the conversion ofthe ester to about 80 mol %, i.e. to effect only a partial hydrolysis tothis extent. Such hydrolysis can be effected with reasonable quantitiesof water. The process of this invention makes it possible to increasethe ester conversion and thus to produce additional quantities ofethylene glycol without problems of increasing conversion in thehydrolysis reaction itself. This is particularly the case when, inaccordance with the preferred embodiment of this invention, thedisproportionation is carried out simultaneously with azeotropicdistillation. By this means, not only is removal of the ethylene glycolwhich is formed as a result of the disproportionation reaction effected,but the ethylene glycol contained in the ester feed to thedisproportionation zone is also effectively recovered, so that anintegrated system for producing ethylene glycol from its lowercarboxylate esters in an efficient manner is provided.

The feed to the hydrolysis operation can be the previously-described"ester feed" or it can consist essentially of the monoester, or of thediester, or of mixtures of mono- and diesters in any proportion. Ingeneral, the reaction continues until an equilibrium mixture comprisingdiester, monoester, ethylene glycol, carboxylic acid and water isformed. Before feeding the hydrolysis reaction product to thedisproportionation reaction, the water and carboxylic acid arepreferably removed from the hydrolysis effluent, e.g. by distillation inany convenient manner, these two compounds being readily separated fromthe ethylene glycol and the lower carboxylic esters. In effecting thehydrolysis, the ethylene glycol lower carboxylate ester, or estermixture, is suitably heated in the presence of water until at least somehydrolysis has occurred. Although the hydrolysis reaction will takeplace solely under the influence of heat, it is preferred, in order toincrease the rate of reaction, to effect hydrolysis in the presence ofan acidic ester hydrolysis catalyst, most preferaby a solid catalyst,e.g. in the form of an acidic ion exchange resin, is employed. Thehydrolysis step is thus suitably carried out by causing the glycol esteror ester mixture to react under the influence of heat (with or without acatalyst) to liberate (i.e. hydrolyze) from 15 to 80 mol % of the acylmoieties, e.g. acetate moieties, as lower carboxylic acid, e.g. aceticacid. At the same time, ethylene glycol is liberated.

In the hydrolysis reaction it is desirable to use at least 0.25 mol ofwater per equivalent of acyl moiety present in the hydrolysis feed.Preferably the amount of water added is in the range of from about 0.75to 5 mols of water per equivalent of acyl moiety in the hydrolysis feed.Of course, greater amounts of water can be used, for example up to 20mols per equivalent of acyl moiety in the hydrolysis feed, but the useof such large amounts of water is both unnecessary and economicallydisadvantageous. It is a feature of this invention that the combinationof a disproportionation operation with the hydrolysis operation makes itpossible to operate the hydrolysis reaction efficiently and effectivelyby using only limited amounts of water since only partial hydrolysis isnecessary.

Hydrolysis reaction temperatures of at least about 50°C. are necessaryin order to obtain economically satisfactory rates of hydrolysis exceptthat, when catalysts are employed, temperatures as low as 25°C. can besatisfactorily used. It is generally not desirable to employ thehydrolysis reaction temperature above about 250°C., however, since athigher temperatures thermal degradation, with concomitant formation ofcolor bodies, can become significant. Preferably temperatures of about50°C. to about 200°C. are employed. Pressure is not, in any manner,critical to the conduct of the hydrolysis and the pressure values givenabove in connection with the disproportionation reaction are suitable aslong as they are sufficient at the prevailing temperature to keep thereaction mixture in the liquid phase. Thus pressures of as little as 50mm. Hg can be employed as also can pressures of several thousand psia.Residence time of reactants and products within the hydrolysis zone isin no way critical as long as the reaction proceeds reasonably near toequilibrium. Thus, for example, residence times from as little as 1minute up to and including several hours, e.g. 4 hours, or longer areentirely feasible.

While any conventional ester hydrolysis catalyst can be used, forexample, materials such as the mineral acids, e.g. hydrochloric,sulfuric and phosphoric acids, and also include organic acids such asoxalic, tartaric and malic acids, as well as such materials astrichloracetic acid and the aryl sulfonic acids, e.g., p-toluenesulfonic acid, it is necessary to separate the catalyst from thehydrolysis effluent, e.g. by distilling the rest of the effluent awayfrom the less volatile catalyst, or by chemical treatment to inactivateor remove the hydrolysis catalyst, before further processing. When suchcatalysts are used, however, they are suitably employed in relativelysmall amounts, e.g. quantities of as little as 0.0001 mol per equivalentof acyl moiety in the feed to the hydrolysis zone being suitable. Largerproportions can be employed though there is little practical reason toemploy amounts greater than about 0.001 mol of acid per equivalent ofglycol moiety in the feed. It is most preferred, therefore, to use solidcatalysts such as acidic ion exchange resins or molecular sieves, e.g.metal alumina silicates (siliceous zeolites) such as molecular sieves ofthe "A" and "X" series, e.g. "Molecular Sieve 4A", and other acidicheterogeneous solid catalysts which can be used in the form of bedsthrough which the feed to be hydrolyzed can be continuously passed, sothat no separation step is necessary. Typical examples of suitable ionexchange resins include cationic exchange resins of the sulfonic acidtype, such as the polystyrene sulfonic acids, exemplified by commercialproducts sold under the names Dowex-50, Duolite C-20, and Ionac Z40.

Following the hydrolysis reaction, the hydrolyzate, which containscarboxylic acid, e.g. acetic acid, and water, in addition to ethyleneglycol, monoesters, and diesters is, as mentioned, suitably passed intoa distillation column wherein a major portion of the carboxylic acid andwater is vaporized and removed as overhead for subsequent recovery. Thisseparation can be carried out in any conventional distillation column.In general, it is desirable to separate at least 90% of the water andcarboxylic acid present in the mixture before proceeding with theremoval and recovery of the ethylene glycol. Although, as mentioned, thedistillation step to separate water and carboxylic acid can be carriedout over a wide range of conditions, it has been found preferable tooperate at pot temperatures of 170° to 240°C. and at pressures of from400 mm. Hg to 50 psig. It will be understood that the water andcarboxylic acid can be removed in a single distillation operation or thedistillation may be carried out in two distillation zones in series withthe water and some of the carboxylic acid being removed in the firstdistillation zone and the remainder of the carboxylic acid to be removedbeing separated in the second distillation zone. This distillation stepis suitably carried out in conventional manner and the selection ofspecific conditions for treatment of specific feeds to separate specificamounts of water and carboxylic acid will be readily apparent to personsskilled in the art.

The invention will be more fully understood by reference to theaccompanying drawing, wherein:

FIG. 1 is a diagrammatic view of a system for carrying out thedisproportionation reaction of the invention simultaneously with removalby distillation of the produced polyhydric compound, illustrated byethylene glycol, and

FIG. 2 is a similar diagrammatic view of an overall system wherein thedisproportionation reaction is integrated with ester hydrolysis,illustrated by ethylene glycol esters.

Referring to the drawing, and more particularly to FIG. 1, an ester feedstream comprising lower carboxylate monoester of ethylene glycol is fedthrough line 10 to disproportionation zone 12 which, in the embodimentillustrated, is a distillation column suitably provided with heatingmeans, e.g. a conventional reboiler or the like (not shown) and with abottoms withdrawal line 14 and an overhead vapor line 16, the latterbeing connected to a condenser 18. The catalyst is introduced throughline 20 so that it may be admixed with the ester feed prior to itsintroduction into the disproportionation zone. The ethylene glycolproduced in the disproportionation reaction which takes place in column12 is removed through line 16, suitably in the form of an azeotrope withan azeotroping agent, and glycol ester is withdrawn through line 14. Theoverhead vapor from column 12 leaves through line 16 and is condensed incondenser 18, flows to a phase-separator 22, and the condensedazeotroping agent is returned to column 12 through line 24 as reflux,whereas the ethylene glycol phase is withdrawn through line 26 and isintroduced into a refining column 28, also provided with any suitableheating means (not shown) wherein ethylene glycol ester and azeotropingagent contained in the ethylene glycol phase withdrawn from phaseseparator 22 is removed as vapor through line 30, and ethylene glycol insubstantially purified form is withdrawn as bottoms through line 32. Thevapors in line 30 are condensed in condenser 34 and a portion isreturned as reflux to column 28 through line 36 and the remainder iswithdrawn through line 38. Some or all of the material in line 38 may becombined with the feed to column 12, and make-up azeotroping agent, asrequired, is also suitably added through line 10 or through line 20.

Referring now to FIG. 2, wherein the disproportionation-azeotropicdistillation system just described is integrated with the hydrolysis oflower carboxylate esters of ethylene glycol to provide the feed todisproportionation column 12, a hydrolysis ester feed stream enters ahydrolysis zone 50 through line 52 and line 54 and water for thehydrolysis enters through line 56 and is combined with the hydrolysisester feed in line 54 before entering zone 50. Zone 50 is suitablyfilled with a bed of solid hydrolysis catalyst, e.g. a bed of acidic ionexchange resin, and the combined water and ester feed stream flowsupwardly through the bed, and the partially-hydrolyzed reaction productis removed through line 58. The product stream in line 58 is introducedinto a water separation column 60, provided with a reboiler or otherheating means (not shown) wherein water is vaporized and, along with asmall amount of carboxylic acid, is withdrawn through line 62 andcondensed in condenser 64. Since in the embodiment illustrated in FIG.2, the condensate from condenser 64 will contain some azeotroping agent,as will be explained below, the condensate passes to a phase separator66 wherein the water and carboxylic acid form one phase and theazeotroping agent forms a second phase, the latter being withdrawn fromseparator 66 through line 68. The aqueous phase is withdrawn throughline 70, with part of it being returned to column 60 through line 72 asreflux and the remainder being recycled to column 50 through line 74which empties into water supply line 56. The portion of the hydrolysisproduct stream supplied to column 60 which is not vaporized andwithdrawn through line 62 and which comprises ethylene glycol,carboxylic acid and lower carboxylate esters of ethylene glycol iswithdrawn through line 75 and fed to a distillation column 76, alsoprovided with appropriate heating means (not shown). In distillationcolumn 76, the carboxylic acid is vaporized and carboxylic acid vaporsare withdrawn through line 78 and condensed in condenser 80 with some ofthe condensate being returned to column 76 as reflux through line 82 andthe remainder being withdrawn from the system through line 84. Thecarboxylic acid stream will also contain any water which was notseparated in column 60. The essentially water-and carboxylic acid-freeethylene glycol-lower carboxylate ester mixture is withdrawn fromdistillation zone 76 through line 86 and is supplied to line 10 toprovide the ester feed to disproportionation zone 12, as described abovein connection with the discussion of FIG. 1. To complete the integrationof the disproportionation system with the hydrolysis system, a line 90connects with line 38 to conduct the withdrawn condensate containingazeotroping agent from column 28 to the feed to hydrolysis zone 50 and aside stream from column 12 comprising vapors of lower carboxylate estersof ethylene glycol is withdrawn through line 92 and also combined withthe feed to the hydrolysis zone, after being condensed in condenser 88.A purge stream comprising liquid esters and catalyst is withdrawnthrough line 14 in order to remove the disproportionation catalyst. Whenthe hydrolysis is carried out thermally, i.e. without the use of ahydrolysis catalyst, then the ester stream from the disproportionationzone to the hydrolysis zone can be a liquid stream, e.g. line 92 can beconnected to line 14 and the disproportionation catalyst will recyclethrough the system. Should any of the disproportionation catalyst reachthe ion exchange resin serving as hydrolysis catalyst, it will beretained by the resin which can then be suitably regenerated to removethe accumulated disproportionation catalyst or it can be replaced fromtime to time. Actually, the solid hydrolysis catalyst will eventuallybecome contaminated with minor amounts of impurities which may becontained in the hydrolysis feed and will need to be regenerated inconventional manner, or replaced.

The following examples of specific application will serve to give afuller understanding of the invention but it will be understood thatthese examples are illustrative only and are not intended as limitingthe invention.

EXAMPLE I

A feed mixture composed of 47.2 wt. % ethylene glycol diacetate (EGDA),46.25 wt. % ethylene glycol monoacetate (EGMA), 6.4 wt. % ethyleneglycol (EG), and 0.15 wt. % of lead acetate is introduced into anOldershaw distillation column consisting of 30 glass trays of 1 inchdiameter above the feed point and 20 trays of 1 inch in diameter belowthe feed point and provided with a 300 cc electrically-heated glassreboiler powered with a Variac set to maintain a constant temperature of189°C. in the reboiler, and the mixture is distilled in the presence ofo-chlorotoluene as azeotroping agent (AA). The overhead vapors (154°C.)are condensed in a sloping glass tube condenser, and the condensedtwo-phase liquid is decanted in a Dean-Stark tube. The heavier liquidcomprising ethylene glycol and ester is drawn off periodically and thelighter liquid comprising the o-chlorotoluene is decanted through theoverflow line and is pumped to the top tray of the column at a fixedflow rate.

During steady state operation 150 cc (approx. 165 g./hr.) of the feedmixture is introduced at the feed point and 170 cc/hr. ofo-chlorotoluene is introduced on the top plate. Most of the AA suppliedis reflux of the lighter liquid to which make-up AA is added tocompensate for that passing into the withdrawn overhead phase. Each houra total of about 31 g. overhead product and a total of about 138 g. ofbottoms product are withdrawn from the column. The analyses of eachproduct are as follows, expressed as wt. %:

               Overhead    Bottoms                                                ______________________________________                                        EG           72.6          0.67                                               EGMA         21.8          23.8                                               EGDA         <0.1          74.1                                               AA           5.5           1.38                                               ______________________________________                                    

Material balance shows that 49.8 percent of the EGMA has been convertedto EG and EGDA and that 63.5 percent of the theoretically attainable EGis in the overhead product. All of the catalyst is in the bottomsproduct and is excluded from the values given above.

EXAMPLE II

The procedure of Example I is repeated except that the feed contains0.25 wt. % lead acetate, using a rate of 150 cc/hr. and ano-chlorotoluene feed of 195 cc/hr. The analyses of the overhead (about36 g.) and bottoms (about 131 g.) products are as follows:

               Overhead    Bottoms                                                ______________________________________                                        EG           71.3          0.31                                               EGMA         22.3          17.0                                               EGDA         <0.1          82.6                                               AA           5.72          <0.1                                               ______________________________________                                    

Conversion of EGMA to ethylene glycol and EGDA is 60.7 and 73.4 percentof the theoretical ethylene glycol is in the overhead.

EXAMPLE III

Using the apparatus described in Example I, the feed mixture of ExampleI, but containing 0.50% lead acetate, was introduced at the rate of 150cc/hr. and o-chlorotoluene is fed to the top plate at the rate of 145cc/hr. Each hour a total of about 24 g. overhead product and a total ofabout 142 g. bottoms product are withdrawn, the analyses of theseproducts, in wt. %, being as follows:

               Overhead    Bottoms                                                ______________________________________                                        EG           87.8          0.37                                               EGMA         7.75          19.7                                               EGDA         <0.1          79.8                                               AA           3.25          <0.1                                               ______________________________________                                    

Material balance shows that 58 percent of the EGMA has been converted toethylene glycol and EGDA and that 75.4 percent of the theoreticallyattainable ethylene glycol is in the overhead product.

EXAMPLE IV

Using apparatus corresponding to that described in Example I, but havingtrays of 2 inch diameter, a feed mixture having the composition of thatused in Example I but containing 0.25 wt. % lead acetate is introducedat the rate of 111 g./hr., and o-chlorotoluene is fed to the top plateat the rate of 130 cc/hr. Each hour a total of about 20 g. overheadproduct and a total of about 90 g. bottoms product are withdrawn fromthe column. The two products analyze as follows in wt. %:

               Overhead    Bottoms                                                ______________________________________                                        EG           79.8          0.14                                               EGMA         14.6          13.7                                               EGDA         <0.1          86.1                                               o-chlorotoluene                                                                            4.53          <0.1                                               ______________________________________                                    

Material balance shows that 70.1 percent of the ethylene glycolmonoacetate has been converted to ethylene glycol and EGDA and that 70.4percent of the theoretically attainable ethylene glycol is in theoverhead product.

EXAMPLE V

Again using the apparatus corresponding to that described in Example I,but having trays of 2 inch diameter, a feed mixture composed of about46.55 wt. % of EGDA, 47.05 wt. % of EGMA, 6.15 wt. % EG and 0.25 wt. %lead acetate is introduced at the rate of 150 g./hr., ando-chlorotoluene is fed to the top plate at the rate of 195 cc/hr. Eachhour a total of about 31 g. overhead product and a total of about 135 g.bottoms product are withdrawn from the column. The two products analyzeas follows, in wt. %:

               Overhead    Bottoms                                                ______________________________________                                        EG           92.6          0.2                                                EGMA         2.93          14.9                                               EGDA         <0.1          84.8                                               o-chlorotoluene                                                                            2.66          <0.1                                               ______________________________________                                    

Material balance shows that 73 percent of the ethylene glycolmonoacetate has been converted to ethylene glycol and EGDA and that 84.7percent of the theoretically attainable ethylene glycol is in theoverhead product.

EXAMPLE VI

A feed consisting of ethylene glycol monoacetate containing 0.1 wt. % oflead acetate is reacted at 180°C. for 15 minutes in a nitrogenatmosphere under a pressure of 100 psig. At the end of this reactionperiod the product mixture is removed from the reaction zone andcontains 5.6 wt. % ethylene glycol, 13.1 wt. % ethylene glycoldiacetate, and 81.3 wt. % ethylene glycol monoacetate.

When either ethylene glycol or ethylene glycol diacetate is removed fromthe mixture, as by solvent extraction or distillation, and the remainingmixture is further reacted, additional amounts of ethylene glycol andethylene glycol diacetate are formed by further disproportionation ofthe ethylene glycol monoacetate.

EXAMPLE VII

A feed consisting of 208 g. ethylene glycol monoacetate containing 0.25wt. % zinc acetate, is introduced near the top of a countercurrentextraction column having 20 extraction stages and maintained at atemperature of 180°C. The feed is passed downwardly countercurrently to600 g. of hexadecane introduced at the bottom of the column and the flowis at a rate to provide an average residence time of about 5 minutes perstage. The hexadecane phase which is removed from the top of theapparatus is composed of approximately 600 g. hexadecane and 130 g.ethylene glycol diacetate, whereas the ethylene glycol phase removedfrom the bottom of the apparatus amounts to 78 g. and is composed of70.5 wt. % ethylene glycol and 29.5 wt. % ethylene glycol monoacetate.

When the processes of the foregoing examples are repeated withcorresponding amounts of trimethyl ammonium acetate, zinc acetate, (leadacetate in the case of Example VII) tetrabutyl tin, dibutyl tindiacetate, cadium acetate, or trimethyl ammonium amine, asdisproportionation catalyst, corresponding disproportionation of themonoester is achieved.

EXAMPLES VIII - XVI

Using the apparatus of Example I, a series of disproportionations arerun using various catalysts. In each case, unless otherwise indicated,the ethylene glycol is removed from the disproportionation zone byazeotropic distillation with o-chlorotoluene and the composition of thefeed is 48 wt. % EGDA, 46 wt. % EGMA, and 6 wt. % EG. The pertinent dataare shown in Table B below.

                                      TABLE B                                     __________________________________________________________________________                  Pot           Head                                                                              Over-                                                   Cat.                                                                              Temp.                                                                             Feed AA   Temp.                                                                             head                                          Example                                                                            Catalyst                                                                           Amt.%                                                                             °C.                                                                        cc./hr.                                                                            cc./hr.                                                                            °C.                                                                        g./hr.                                        __________________________________________________________________________    VIII TMAA 0.15                                                                              189 150  195  151 28                                            IX   ZA   0.25                                                                              186 150  195  154 37                                            X    TBT  0.2 191 150  200  155 28                                            XI   TBT  1.5 190 150  200  156 32                                            XII  DBTDA                                                                              3   187 150  200  154 32                                            XIII CA   0.15                                                                              191 150  195  155 34                                            XIV  LA   0.05                                                                              189 150  195  154 32                                            XV*  LA   0.15                                                                              185 150  140  160 34                                            XVI* LA   0.05                                                                              189 150  140  162 29                                            __________________________________________________________________________              Overhead         Bottoms                                                      Composition, Wt. %                                                                             Composition, Wt. %                                                                           EGMA                                Example                                                                            Catalyst                                                                           EG  EGMA                                                                              EGDA                                                                              AA   EG  EGMA                                                                              EGDA                                                                              AA Conversion(%)                       __________________________________________________________________________    VIII TMAA 70.3                                                                              21.2                                                                              tr. 8.4  tr. 27.1                                                                              72.9                                                                              tr.                                                                              45                                  IX   ZA   57  34.2                                                                              tr. 8.8  0.4 29.1                                                                              70.5                                                                              tr.                                                                              61.9                                X    TBT  53.7                                                                              35.8                                                                              tr. 10.5 tr. 27.5                                                                              72.5                                                                              tr.                                                                              50.3                                XI   TBT  58.9                                                                              35.2                                                                              0.3 5.6  tr. 25.6                                                                              74.4                                                                              tr.                                                                              54.1                                XII  DBTDA                                                                              75.8                                                                              18.3                                                                              tr. 5.8  tr. 16.5                                                                              83.5                                                                              tr.                                                                              70                                  XIII CA   63.6                                                                              29  tr. 7.3  tr. 20.3                                                                              79.7                                                                              tr.                                                                              64.6                                XIV  LA   67  26.3                                                                              tr. 6.7  tr. 23.4                                                                              76.6                                                                              tr.                                                                              63.1                                XV*  LA   70.9                                                                              24.4                                                                              tr. 2.6  tr. 15.4                                                                              84.5                                                                              tr.                                                                              58.2                                XVI* LA   78.7                                                                              18.6                                                                              tr. 2.7  tr. 16.9                                                                              83.1                                                                              tr.                                                                              61.7                                __________________________________________________________________________    TMAA = Trimethyl Ammonium Acetate                                             ZA  = Zinc Acetate                                                            TBT = Tetrabutyl Tin                                                          DBTDA = Dibutyl Tin Diacetate                                                 CA  = Cadmium Acetate                                                         LA  = Lead Acetate                                                            *Pseudocumene azeotroping agent; feed comprising (wt. %) 51.6 EGDA, 44.6      EGMA, 3.8 EG.                                                             

EXAMPLE XVII

A combined hydrolysis-disproportionation system as illustrated in FIG. 2is used for continuously hydrolyzing an ester mixture containing someethylene glycol and composed of approximately 54 mol % of ethyleneglycol diacetate, 41 mol % of ethylene glycol monoacetate, and 5 mol %ethylene glycol, and subsequently disproportionating the ethylene glycolmonoacetate and recovering ethylene glycol from the system. Thefollowing discussion relates to the operation of this system aftersteady state conditions are attained.

The fresh feed mixture is introduced through line 56 at a rate toprovide, per hour, 244.7 lb. mols EGDA, 184.9 lb. mols EGMA, and 24.4lb. mols EG, and this mixture is combined with recycle streams 90 and 92to provide a flow of approximately 1088 lb. mols/hr. EGDA and 185 lb.mols/hr. EGMA, and 34.8 lb. mols/hr. EG, into hydrolysis zone 50, whichis maintained at a temperature of 90°C. and consists of about an 800cubic foot bed of 100 to 200 mesh Dowex 50W-X8 ion exchange resin. Atthe same time water is introduced at the rate of approximately 656.4 lb.mols/hr. make up water and approximately 530.9 lb. mols/hr. recyclewater containing a small amount of acetic acid. The partially-hydrolyzedproduct (about 52 percent of the EGDA fed to the hydrolysis zone remainsunconverted) is withdrawn through line 58 and passed to the 9th platefrom the top of column 60 which contains 53 actual plates and isoperated at a reboiler temperature of about 152°C. and at substantiallyatmospheric pressure, with a reflux ratio of 2:1 to separate as overheadthe water-acetic acid recycle stream and a bottoms stream comprising theremainder of the hydrolysis effluent which is passed onto the 12th platefrom the top of column 76 which has 28 actual plates and is operated ata reboiler temperature of 182°C. and at atmospheric pressure, with areflux ratio of 1.6:1. Azeotroping agent in recycle stream 90 is removedin separator 66 and returned to column 12 through line 68. In column 76the remainder of the acetic acid and water are separated and withdrawnthrough line 84. The bottoms product from column 76, comprising theester and glycol components of the hydrolysis reaction, has added to itlead acetate at the rate of approximately 0.24 lb. mol/hr. and themixture is introduced to the 20th plate from the top of the azeotropicdistillation column 12 which contains 55 actual plates and employso-chlorotoluene as azeotroping agent which is continuously recycled tothe column through lines 24 and 68 and is present in an amount toprovide a ratio of azeotroping agent to ester-glycol feed ofapproximately 1.9:1. All of the azeotroping agent condensed andseparated in separator 22 is returned to column 12 and the ethyleneglycol phase from separator 22, which contains approximately 4 mol %o-chlorotoluene, 19 mol % EGMA, and is free from EGDA, is fed torefining column 28 which contains 60 actual plates and is operated at areboiler temperature of 173°C. and at a pressure of 200 mm. Hg with areflux ratio of 7:1 and there is obtained a bottoms product consistingessentially of ethylene glycol, which is withdrawn at the rate ofapproximately 444 lb. mols/hr., and the net overhead, as previouslymentioned, is recycled to the hydrolyzer through line 90. An ester purgestream of 9 lb. mols/hr. (calculated as ethylene glycol diacetate) andcontaining the catalyst is withdrawn through line 14 and can beprocessed for catalyst recovery, if desired and the catalyst recycled toline 20. A vapor stream composed substantially entirely of EGDA iswithdrawn through line 92 from above the 53rd plate from the top ofcolumn 12 and, after condensation in condenser 88 provides thepreviously-mentioned recycle stream. In the foregoing example there wassubstantially 85-90 percent conversion of EGMA to EG and EGDA.

In the foregoing example, the hydrolysis feed contains ethylene glycoland a substantial amount of ethylene glycol monoester which isrepresentative of a feed which would normally be available from theprocessing of a carboxylate ester product produced by the reaction ofacetic acid and ethylene, but corresponding effective operation is alsorealized when this example is repeated with a feed containingessentially no ethylene glycol or lesser amounts of ethylene glycolmonoacetate or composed essentially of ethylene glycol diacetate. Suchfeeds require appropriate adjustment in the operation of thedistillation units as will be obvious to persons skilled in the art.Ethylene glycol which is recovered as the product of this process is ofhigh-purity such that it can be used directly in the production offiber-grade polyesters.

What has been said above with regard to the treatment of lowercarboxylate esters of ethylene glycol and with respect to the productionand recovery of ethylene glycol also applies, as previously indicated,to the treatment of lower carboxylate esters of other polyhydriccompounds of the character specified above. Thus, when Example VI, forinstance, is repeated using propylene glycol monoacetate, or themonoacetate of 1,4-butane diol, or the monoacetate of 1,2-butene diol,or the monoacetate, of catechol, or the diacetate of glycerol,corresponding results are achieved and effective production of the freepolyhydric compound is realized. In like manner, corresponding resultsare obtained when the esters of other lower alkanoic acids are used inplace of the acetic acid esters, for example the formates andpropionates. It is intended, therefore, that all matter contained in theforegoing description shall be interpreted as illustrative only and notas limitative of the invention.

I claim:
 1. A process which comprises the steps of:a. subjecting atleast one lower alkanoic diester of an alkane diol containing 2 to 6carbon atoms to partial hydrolysis with water in a hydrolysis zone tohydrolyze at least part of said ester to produce a hydrolysis productcomprising said diol, alkanoic acid, water and lower alkanoic monoesterof said diol, b. distilling said hydrolysis product to vaporize a majorportion of said water and said alkanoic acid away from said diol andsaid ester to produce a bottoms mixture comprising said diol and saidlower alkanoic monoester, c. introducing said bottoms product into areaction zone, d. heating said bottoms product in said reaction zone ata temperature within the range of room temperature up to about 280°C inthe presence of a basic disproportionation catalyst which is a weak baseor a substance which forms a weak base in situ in the presence of saidlower alkanoic ester employed in the amount of 0.001 to 5% by weightbased upon the free hydroxyl-group-containing lower alkanoic ester inthe feed to convert at least some of said lower alkanoic monoester tosaid diol and to a lower alkanoic diester of said diol, and e.recovering said thus-produced diol from said reaction zone.
 2. A processas defined in claim 1, wherein said hydrolysis is carried out in thepresence of a solid hydrolysis catalyst to produce a hydrolysis productcomprising diol, alkanoic acid, water and alkanoic mixture of loweralkanoic mono- and diester of said diol.
 3. A process as defined inclaim 1, wherein step b) is carried out in two distillation zones, thewater being primarily removed in the first of said two distillationzones and the alkalnoic acid being primarily removed in the second ofsaid two distillation zones.
 4. A prcess as defined in claim 1, whereinsaid diol is ethylene glycol.
 5. A process as defined in claim 1,wherein each ester is an acetate.
 6. A process as defined in claim 5,wherein said diol is ethylene glycol.